JPH06194114A - Capacitance sensor - Google Patents

Abstract

PURPOSE:To detect film thickness and the like more correctly in the contactless state. CONSTITUTION:An inner electrode 3 and an outer electrode 2 of such a shape as to surround the inner electrode 3 are disposed on one face of a sheet-like substrate 1 made of an insulating material. The capacitance between the inner and outer electrodes is changed according to the thickness of a liquid film generated on the other face of the sheet-like substrate 1, and output voltage corresponding to this capacitance can be obtained. A sensor capable of detecting film thickness correctly can be, thereby, obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a capacitance sensor used for measuring the film thickness of liquid.

[0002]

2. Description of the Related Art A typical one of this type of capacitance sensor is shown in FIG. this is,
By providing a flat-plate counter electrode 13 facing the flat-plate electrode 11 and measuring the capacitance between them, the electrode 13
This is a capacitance sensor that detects the film thickness of the DUT 12 existing above.

[0003]

However, in the above method, since it is necessary to provide a pair of flat plate electrodes facing each other, various methods are required for measuring the film thickness of a liquid on a substrate typified by an automobile windshield. However, it is extremely difficult to put it into practical use. The present invention has been made in view of these points, and an object thereof is to provide a capacitance sensor having less restrictions than the conventional one, and to more accurately detect the film thickness of a liquid in a face piece or a tube body. It is a thing.

[0004]

In order to achieve the above object, according to the present invention, an inner electrode and an outer electrode surrounding the inner electrode are arranged on one surface of a planar substrate made of an insulating material. . In this case, it is desirable to use the inner electrode as the anode and the outer electrode as the cathode, respectively.

[0005]

In the present invention, the electric field is formed between the inner electrode and the outer electrode arranged on one surface of the planar substrate, and the distribution state thereof is the thickness of the liquid film formed on the other surface of the substrate. And the capacitance between both electrodes changes. Since the change in capacitance is detected as an increase or decrease in the output voltage, the film thickness of the liquid can be detected by comparing it with a reference value measured in advance.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The illustrated embodiments will be described below. Figure 1
In FIG. 1, 1 is a planar substrate made of an insulating material such as a glass plate or an acrylic plate, 2 and 3 are outer electrodes and inner electrodes formed on one surface of the planar substrate 1, and the planar substrate 1 is a flat surface. Alternatively, it may be a curved surface. The electrodes 2 and 3 are formed by, for example, adhering an aluminum foil or applying a conductive paint, and are formed in a ring shape in which the outer electrode 2 is closed so as to surround the circular inner electrode 3 as shown in the figure. Reference numeral 4 denotes a liquid film existing on the surface of the planar substrate 1.

This embodiment can be used to measure the film thickness of a conductive liquid formed on an insulating substrate, such as a water film on the surface of a windshield of an automobile. That is, the distribution of the electric field formed between the outer electrode 2 and the inner electrode 3 changes depending on the thickness of the liquid film 4 on the planar substrate 1, and the capacitance between the electrodes 2 and 3 changes accordingly. Therefore, the film thickness can be detected by comparing it with the reference value measured in advance.

The embodiment of FIG. 1 is suitable for local measurement in a narrow range, but the electrodes 2, 3 are elongated as shown in FIG. 2 to measure an average value in a relatively wide range. A sensor suitable for is obtained. Further, by arranging the sensor shown in FIG. 2 in the tube axis direction on a long tube or vertically on the wall surface of the liquid tank, it can be used for detecting the liquid level. 1 and 2, the electrode 2 is used as the cathode and the electrode 3 is used as the anode. As a result, the shield effect is generated in the electrode 2 and the disturbance is absorbed by the outer electrode, and the electric field formed between the electrodes 2 and 3 is less likely to be affected. Furthermore, it becomes difficult to detect originally unnecessary data outside the sensor range, and it is possible to prevent a large error in the measurement result.

In the embodiment shown in FIGS. 1 and 2,
It is not possible to distinguish from the output voltage whether the liquid film on the planar substrate 1 is formed with a uniform film thickness and when it is distributed in the form of droplets. Since it is known in advance from the type of measurement object, measurement conditions, etc., there is no problem in measurement.

[0010]

As is apparent from the above description, according to the present invention, the inner electrode and the outer electrode surrounding the inner electrode are arranged on one surface of the planar substrate made of an insulating material. Therefore, it is possible to measure the film thickness of the liquid generated on the planar substrate without being restricted by the sensor mounting position and posture due to its structural characteristics and without hindering the generation of the liquid film. Become. In particular, in the case where the inner electrode is used as an anode and the outer electrode is used as a cathode, the shielding effect is exerted, the influence of disturbance is less likely to occur, and the measurement accuracy is improved.

[Brief description of drawings]

FIG. 1 is a sectional view and a plan view of an embodiment of the present invention.

FIG. 2 is a plan view showing an electrode arrangement according to another embodiment.

FIG. 3 is a vertical sectional view of a conventional example.

[Explanation of symbols]

 1 planar substrate 2 outer electrode 3 inner electrode

Claims (2)

[Claims] 1. A capacitance sensor, wherein an inner electrode and an outer electrode having a shape surrounding the inner electrode are arranged on one surface of a planar substrate made of an insulating material. 2. The capacitance sensor according to claim 1, wherein the inner electrode is an anode and the outer electrode is a cathode.